When the packing material is loaded into the packing chamber, it is axially compressed by the gland screw. When the shaft moves relative to the packing material, the packing material produces radial force due to its plasticity and is in close contact with the shaft.At the same time, the impregnated lubricant in the filler is extruded to form an oil film between the contact surfaces.Since the contact state is not particularly uniform, "boundary lubrication" occurs at the contact position, which is called "bearing effect".However, small oil groove is formed in the uncontacted concavity, with thicker oil film. The contact part and non-contact part form an irregular maze, which ACTS as the prevention of leakage of liquid flow. This is called "labyrinth effect".This is how the packing seal works.Obviously, good sealing depends on maintaining "bearing effect" and "labyrinth effect".That is, maintain good lubrication and proper compaction.If the lubrication is not good, or the pressure is too tight, the oil film will be interrupted, resulting in dry friction between the packing and the shaft, which eventually leads to burning shaft and serious wear [2].

For this reason, the packing's compaction level needs to be adjusted frequently so that the lubricant in the packing can squeeze out some more lubricant after a period of running and compensate for the relaxation of the packing due to volume changes.Obviously, this often squeezes the filler, which will eventually dry out the impregnant, so it is necessary to replace the filler on a regular basis.In addition, in order to maintain the liquid film and to take away the heat of friction, it is also necessary to intentionally allow a small amount of leakage at the filler.